(1) Field of the Invention
The technology disclosed herein relates to a cleaning member and an image forming apparatus using this, in particular relating to a cleaning member for cleaning developers (toner) and paper dust remaining on the outer peripheral surface of a fixing roller and an image forming apparatus for forming image information on a recording medium by electrophotography wherein the fixing roller is adapted to be cleaned by the cleaning member.
(2) Description of the Prior Art
Recently, in the field of image forming apparatuses based on electrophotography, there has been a trend of the developer (toner) becoming smaller in particle size in order to support high-speed printing jobs and promote improvement in print quality.
For example, high-speed print processing in the image forming apparatus conventionally indicated a printing operation for 40 to 60 sheets per minute for standard paper (A4 short-edge feed). But development into a high-speed, configuration handling 100 or greater sheets per minutes, which used to be the field of mimeograph, is in progress.
In an image forming apparatus supporting high-speed processing, in order to increase the number of processing, the rotational speeds of the photosensitive member etc., and the conveyance speed of recording media have to be made faster than that in the conventional configuration, so the speed should need to be enhanced about 1.5 times as high as the conventional operating speed (about 450 mm/sec at maximum).
However, with the high-speed development of the image forming apparatus, there occur various problems as follows.
For example, concerning paper feed, there occurs a problem of a greater amount of paper dust arising compared to the conventional configuration.
Usually, the paper stored in the paper feed cassette is picked up sheet by sheet by the pickup roller and conveyed passing through the transfer station and the fixing unit by means of feed rollers, then discharged to the paper output tray. In this process, the paper dust that has been tribo-electrified when picked up by the pickup roller separates into two parts, under the influence of the transfer electric field; that is, some paper dust remains on the paper, the other transfers to the photosensitive drum through the transfer station, and these are believed to be the cause of the most of the above problems.
To deal with such paper dust, a proposal (Japanese Patent Application Laid-open 2001-83831) has been proposed which attempts to secure print quality by removing paper particles with a cleaning element on the photosensitive member.
However, in the field of the image forming apparatuses for supporting high-speed operation, there has been a problem in that the ratio (content) of paper particles remaining on the paper and transferring to the photosensitive member by the transfer electric field changes due to high paper feed speed.
More specifically, since the paper passes through the transfer station at high speed in the process of high-speed printing, short fibers of the pulp component (that is the main component of paper dust) are made to transfer to the photosensitive member under the influence of the transfer electric field as in the conventional configuration while the pulp component of relatively long fibers will remain on the paper because of being less affected by the transfer electric field.
On the other hand, in the fixing step (fixing mechanism) as the step after the transfer step, the fixing rollers that constitute the fixing mechanism are rotationally driven by a rotational force from a drive source. The fixing rollers are made up of a heat roller and a pressing roller, and there are cases where tribo-electricity is generated by friction at the nip between these rollers. If the paper carrying paper dust is conveyed into the fixing stage under this condition, paper dust on the paper will transfer to these two rollers.
Incidentally, the developers (unfixed toner) having transferred to the paper contain an increased amount of a lower charged toner component compared to the amount of charge on the toner used in a conventional machine because of execution of high-speed printing operations. This is caused by the fact of high rotational speeds of the rotational bodies in the developing hopper such as an agitating roller, supply roller, developer sleeve etc, and by the fact of the charge on the toner being unable to reach saturation due to lower agitation performance because of increase in toner consumption by high speed printing, and by other reasons.
The visual images (image information) formed on the photosensitive member with such toner suffer from a printing problem in that toner is scattered around image patterns in the print by the transfer electric field.
Since the thus scattered toner is present individually or particle by particle on the paper, this toner is more likely to transfer to the heat roller in the fixing stage, compared to the toner that form a dot consisting of clustered toner particles. This is because toner particles in the cluster that forms a dot exchange heat with each other as receiving heat from the heat roller and join to each other under the fused condition, producing an increased binding force to the paper (an increased sticking effect).
On the other hand, the individual toner particles that will not form a dot also receive the same amount of heat from the fixing roller (heat roller), but are not affected by neighboring toner particles, so that they are fused but cannot reach the level that produces adequate sticking effect hence will transfer to the heat roller side.
In the above way, when excess fiber pulp (paper dust) and toner (developers) adhere to the fixing rollers, there occurs the problem that cleaning load in the cleaning portion of the fixing rollers is increased compared to that in the conventional machine.
In addition, the cleaning configuration for the conventional fixing rollers uses a roller type with a roller of felt and/or metal, a blade type with a blade of heat-resistant hard rubber, or the like. Any of these methods involves insufficient toner collecting performance and the lifetime problem as a cleaning member for the fixing rollers in high-speed machines when considering increase in cleaning quantity and the usage status of the high-speed machine.